The invention pertains to power transmissions, drive couplings, or clutching mechanisms of the type which utilize clutches with helical cam actuators for transmitting power between power transmitting rotatable shafts. Such prior devices have limitations because of their inability to transmit power selectively in opposite directions through the transmission, inability to absorb sufficient energy without deterioration of the type of clutch employed thus preventing shifts at high speeds and loads, requiring close dimensional control in the manufacturing processes of the parts, lack of uniform quality of engagement of the clutches, and furthermore, engagement and disengagement often difficult and variable from one clutch to another. Still other prior art devices were such that spiral splines were used but required both right hand and left hand splines for reversing the direction of rotation of the transmission which resulted in cumbersome and expensive construction, and required different parts for any particular direction of input rotation.
Some examples of prior art devices in general are shown in the U.S. Pat. No. 3,977,503 which issued Aug. 31, 1976 and entitled "Clutch" and in the U.S. Pat. No. 3,135,129 which issued June 2, 1964 and entitled "Reversing Gear."